1. Field of the Invention
The present invention relates generally to medical devices and methods. More particularly, the present invention relates to apparatus and methods for removing air from vascular and other medical catheters having chambers which are filled with liquid.
Balloon angioplasty, stent treatment, and numerous other intravascular procedures employ catheters which are introduced to the vasculature and advanced intravascularly to a target location, often in the coronary vasculature. Many such intravascular catheters have inflatable balloons and other structures intended to effect or assist in performing a therapeutic procedure, e.g. balloon angioplasty, stent placement, and/or drug delivery. Such expandable structures can take a variety of forms, including non-distensible balloons of the type typically used for performing angioplasty, elastomeric balloons of the type often used for vessel occlusion, and driving structures of the type used for advancing needles and manipulating other tools.
Because of the dangers of the release of air into the bloodstream, such expandable structures are typically inflated with a liquid, such as saline, in order to achieve inflation within the vasculature. In order to purge the inflatable structures prior to use, the catheters are typically primed with liquid immediately prior to use. A common method of priming relies on vacuum aspiration of air from the inflatable structure through a lumen in the catheter, typically the inflation lumen which is subsequently used to introduce the liquid inflation medium. Thus, a vacuum is typically applied through the inflation lumen to lower the air pressure within the inflatable structure to a fraction of atmospheric pressure, typically 15 mm Hg or below. A liquid inflation medium is then introduced into the inflatable structure while preventing the reintroduction of air and other gasses.
While this procedure significantly limits the presence of air and other gasses within the inflatable structure, it will be appreciated that there will usually be a small residual amount of gas within the inflatable structure since the vacuum drawn is not complete. In order to even further enhance the safety, it is desirable to reduce or eliminate such residual gas amount within the inflatable structure.
The most common method for eliminating such residual gas in the balloon or other inflatable structure is to provide a vent tube or hole from the interior of the inflatable structure to the atmosphere. In this way, as the balloon or other inflatable structure is primed with liquid inflation medium, the residual air or gas will migrate toward the vent and be released into the atmosphere. The release of liquid medium is reduced or eliminated by providing vent tubes or holes having small or capillary dimensions. Thus, the vent tubes or holes will allow gas to pass but will inhibit the passage of the liquid inflation medium at the priming pressures and subsequent therapeutic pressures used in the procedures.
While the use of vent tubes and holes has been generally successful, the need to provide a passage from the interior of the inflatable structure to the atmosphere can compromise the integrity and design of the inflatable structure. Thus, it would be desirable to provide alternative and improved structures for removing or sequestering residual gas inside an inflatable structure on a vascular or other catheter prior to use. In particular, it would be desirable if the apparatus and methods did not require significant alteration in the structure of the balloon or other inflatable structure on the catheter. Some of these objectives will be met by the invention described herein below.
2. Description of the Background Art
Vascular catheters having balloons with vent structures are described in U.S. Pat. Nos. 4,638,805; 4,692,200; 4,715,378; 4,810,455; 4,821,722; 5,035,705; 5,049,130; 5,100,385; 5,176,698; and 5,256,143.